1. Field of the Invention
This invention relates to a process for determining the radius of curvature of the cornea of an eye, and more particularly, to a method for fitting contact lenses.
2. Description of the Prior Art
Prior art techniques for fitting a contact lens to the corneal surface of a human eye involve either trial and error techniques or the use of complicated and expensive devices. These available prior art devices are difficult to use and require a considerable amount of time to generate the desired cornea curvature data.
A prior art device known as a keratometer has the capability of measuring the radius of curvature of the cornea in a three to four millimeter diameter area in the vicinity of the pupil of the eye. The accuracy of measurements made by using a keratometer depend on the ability of a patent to properly focus his eye at a particular point.
In contact lens fitting procedures, one must determine the physical contour or shape of the rear surface of the contact lens so that the rear surface of the lens will have the same contour as the curved outer surface of the cornea itself. In addition, one must determine the optical characteristics of the lens which are required to compensate for the irregularities in the cornea.
The cornea of a human eye includes a centrally located optical zone which is positioned above the pupil of the eye. Light rays transmitted into the interior of the human eye pass through and are refracted by the optical zone of the eye. A corresponding optical zone in a contact lens is provided to obtain the required optical compensation for irregularities in the optical zone of the cornea. A contact lens also includes a bearing zone located concentrically around the optical zone, the lens bearing zone assists in securing the rear surface of the lens to the cornea of the eye and provides a bearing surface which supports the contact lens in front of the cornea.
Properly fitting a contact lens to a patient involves determining the proper contour of the rear surface of the optical zone of the lens as well as the contour of the rear surface bearing zone of the lens. Typical human corneas include an optical zone which can generally be approximated by a section of a sphere while the section of the cornea corresponding to the bearing zone of the lens has a flatter curvature.
The prior art discloses a variety of devices intended to determine the curvature of the cornea of an eye for the purpose of fitting contact lenses. U.S. Pat. No. 3,756,702 (Trachtman) discloses a method for producing precisely fitted contact lenses by generating an exact, enlarged photographic profile of the eye. This photographic profile of the eye is used to create a template for the curvature of the rear surface of a contact lens which precisely conforms to the shape of the cornea of the eye.
U.S. Pat. No. 3,285,512 (Reynolds) discloses a graphical corneal contact lens computer which permits a viewer to determine by superposition an appropriate contour for the rear surface of a contact lens which will approximately match the cornea curvature.
U.S. Pat. No. 3,510,207 (Neefe) discloses a method for fitting aspheric contact lenses. The Neefe method utilizes two different specialized lenses during his fitting procedure. The first lens includes an opaque area located at the center of the lens which occupies approximately half of the area of a dilated pupil. A second opaque lens includes a transparent aperture located at its center which also occupies half the area of a dilated pupil. Refractive measurements taken when an individual wears each of these two lenses assists in determining the shape of a contact lens.
U.S. Pat. No. 3,482,904 (Bolk) measures the eccentricity of a cornea by reflecting an image of a target from a predetermined area of the cornea which is viewed at an angle by a specialized telescopic instrument.
U.S. Pat. No. 3,937,566 (Townsely) discloses a method for producing contact lenses and involves the use of a keratometer.